One common application for thermal sensors is in thermal (infrared) imaging devices such as night vision equipment. One such class of thermal imaging devices includes a focal plane array of thermal sensors having thermal sensitive elements. The focal plane array and its associated thermal sensors are often coupled to an integrated circuit substrate with a corresponding array of contact pads and a thermal isolation structure disposed between the focal plane array and the integrated circuit substrate. The thermal sensors typically define the respective picture elements or pixels of the resulting thermal image.
One type of thermal sensor includes a thermal sensitive element formed from pyroelectric material, such as barium strontium titanate (BST), that exhibits a state of electrical polarization and/or change in dielectric constant dependent upon temperature changes of the pyroelectric material in response to incident infrared radiation. For one such thermal sensor, an infrared absorber and common electrode assembly may be disposed on one side of the associated thermal sensitive element. A sensor signal electrode may be disposed on the opposite of the thermal sensitive element. The infrared absorber and common electrode assembly typically extends across the surface of an associated focal plane array and is attached to the thermal sensitive element of each thermal sensor in the focal plane array. Each thermal sensitive element preferably has its own separate sensor signal electrode. The common electrode and the sensor signal electrode constitute capacitive plates. The pyroelectric material constitutes a dielectric or insulator disposed between the capacitive plates.
Such thermal sensors are often incorporated into thermal imaging systems using hybrid solid state fabricating techniques. For some thermal sensors barium strontium titanate (BST) may be used to form the associated thermal sensitive elements. The starting place for fabricating such thermal sensitive elements is typically a wafer of barium strontium titanate or other suitable pyroelectric material having a diameter of approximately 4 inches and an approximate thickness of 0.1 inches. Various grinding and/or polishing processes are frequently used to reduce the thickness of the BST wafer to approximately 0.001 inches or less. The resulting focal plane array of thermal sensors formed from such pyroelectric material may be coupled with an integrated circuit substrate using bump-bonding procedures or other techniques associated with fabricating hybrid solid state systems.